RDMA/erdma: Prevent use-after-free in erdma_accept_newconn()

After the erdma_cep_put(new_cep) being called, new_cep will be freed,
and the following dereference will cause a UAF problem. Fix this issue.

Fixes: 920d93e ("RDMA/erdma: Add connection management (CM) support")
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/hw/erdma/erdma_cm.c

@@ -709,7 +709,6 @@ static void erdma_accept_newconn(struct erdma_cep *cep)
 		erdma_cancel_mpatimer(new_cep);
 
 		erdma_cep_put(new_cep);
-		new_cep->sock = NULL;
 	}
 
 	if (new_s) {